1. Field of the Invention
This invention relates to measuring devices utilizing variable color analog display.
2. Description of the Prior Art
Monochromatic analog display devices for displaying information in a bar graph format are well known and extensively used. Commercially available bar display array usually consists of ten matched LEDs of the same color. Multicolor bar display arrays are also known that contain combinations of red, green and yellow LEDs arranged in a predetermined sequence. Such color sequences are fixed and cannot be changed.
It is feasible to construct a simple analog voltmeter for visually indicating the level of a measured signal by combining a monochromatic bar display array with a suitable bar or dot driver chip. Such a voltmeter, however, is capable of indicating only the measured value; it is not capable of simultaneously indicating the measured value and its relation to measurement limits.
A device for producing an illuminated band representation of measured voltage is disclosed in U.S. Pat. No. 3,961,256 issued on June 1, 1976 to Colin Simister Gaskell et al. The device relies on analog comparators for comparing the measured value with predetermined limits. When the measured value is within the limits, the band is fully illuminated, without simultaneously indicating the limits. When the measured value exceeds the limits, the portion of the band below the low limit is fully illuminated, the portion of the band between the limits is flashed on and off, to attract attention of an operator, and the portion of the band above the high limit is extinguished, to indicate the limit points, without simultaneously indicating the actual measured value.
Such a concept is not usable in a moving dot type display voltmeter wherein the value of measured voltage is indicated by the position of a single illuminated LED, because it is impossible to simultaneously fully illuminate the single LED, flash it on and off, and extinguish it.